1. Field of the Invention
The present invention relates to flat cathode ray tubes (hereafter xe2x80x9cCRTxe2x80x9d), and more particularly, to flat CRTs.
2. Background of the Related Art
CRT""s are the most common type of display system used in homes, offices, and industrial sites. Modern CRT displays incorporate relatively flat and large sized display screens. Such flat and large CRTs are especially applicable to a multimedia environment in accordance with the development of display technologies and changes in consumer""s tastes. As the variety of information media expands and uses of CRTs for displays increase, the demand for flat CRTs which minimize distortion of the displayed image increases.
In general, a CRT display is designed to have identical curvatures on both the inside and outside surfaces of the panel. The outside surface curvature causes a distortion of the displayed image. This distorted picture is difficult to view and the reflection of stray light at the panel surface causes glare which causes eye fatigue.
Since the glass surface of the display panel of a CRT is smooth, the glass surface can reflect external light causing unwanted glare. This glare from the display panel causes eyestrain and eye fatigue in the viewer, and also interferes with viewing the display panel and causes image degradation. Additionally, the CRT is formed of non-conductive glass, which allows a buildup of static electricity on the glass surface. To ameliorate the problems of glare and static charge buildup, in general, a silica base solution containing a conductive metal oxide, such as indium tin oxide (hereafter xe2x80x9cITOxe2x80x9d), and a low reflectivity silica base solution are spin coated on the external surface of the display panel in succession, for not only reducing glare, but also for shielding static electricity and as an anti-reflection coating for electromagnetic waves. The anti-reflection properties are achieved through an offsetting effect of the two layers which causes reflected light to be cancelled through interference.
In the spin coating process, the display panel is fitted to a spin coater, and held in place by a vacuum pad, in which the display panel is affixed in place with vacuum by a vacuum chuck. Alternatively, the display panel can be held by a disk plate method, in which the display panel is fitted into a recess in a holding plate formed to receive the panel. After the panel is either fitted in the vacuum chuck or in the disk plate, it is spun within a chamber, while a coating liquid is dropped onto the display panel to form an anti-glare, anti-static and anti-reflective coating.
FIG. 1 is a schematic illustration of a related art method for spin coating a glass display panel, with the aforementioned solutions, by the disk plate method. In FIG. 1, the spin coater 10 includes rotating part having a fixed chamber 15, and a disk plate 25 fitted at the center of the chamber 15. The disk plate 25 is rotated by a motor 20. A coating solution feeder 30 over the disk plate 25 includes a pressurized coating solution tank 32, a connection tube 36 with a regulator 34, and a nozzle 38. The disk plate 25 has a recess formed to receive the display panel 5, and into which the display panel 5 is mounted. The rotational velocity of the disk plate 25 is controlled by a rotations per minute hereafter xe2x80x9cRPMxe2x80x9d) controller (not shown) connected to the motor 20.
In operation, while the display panel 5 mounted on the disk plate 25 is rotated at a fixed RPM by the motor 20, the coating solution 40 flows from the pressurized coating solution tank 32 and is deposited onto the rotating display panel 5 through the nozzle 38. The amount of coating solution deposited on the display panel 5 is regulated by the regulator 34.
In order to reduce the problems exhibited by CRTs with curved surfaces, a panel having a flat outside surface has been developed. The panel with a flat outside surface (hereafter xe2x80x9cFCDxe2x80x9d) is a structure which aids in forming a flat image by eliminating picture distortion at certain viewing distances and by accommodating different viewing positions to reduce viewer eye fatigue. However, the FCD is thinner near the center of the CRT display, and thicker near the edges specifically, the FCD has a thickness ratio from center to periphery of greater than approximately 170%. Due to the relatively large thickness ratio, the transmissivity of FCD, relative to the image forming light, varies between the center and the periphery of the CRT display panel.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide a flat CRT with substantially improved viewability.
Another object of the present invention is to provide a flat CRT in which a thickness of an antireflection and/or antistatic coating on an outside surface of a display panel is varied as a function of location, not only for antireflection, antistatic, and electromagnetic shielding, but also for elimination of transmissivity variations that are caused by the increased thickness ratio that results as the panel is made flatter.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the flat CRT includes a display panel having a substantially flat outside surface, an inside surface with a fixed curvature, and a film coating on the outside surface of the display panel for antireflection and/or for reducing static electricity, wherein a display panel thickness ratio between the display panel edge and the display panel center is greater than approximately 170%. In addition to the film coating thickness being different between the panel""s center and the panel""s edge, the film coating thickness changes smoothly and gradually from the panel""s center to the panel""s edge.
The difference of film coating thickness preferably varies between the panel""s center and the panel""s edge part is approximately 10-35 nanometers (hereinafter xe2x80x9cnmxe2x80x9d), or approximately 15-30 nm. The film coating transmissivity, y, at different positions across the surface of the panel on the diagonal, long, and short axes can be expressed according to the following equations:
for the diagonal axis A: 0.8624x2xe2x88x922.0957x+73.71xe2x89xa6yxe2x89xa60.8643x2xe2x88x922.0957x+76.72, 
for the short axis B: 0.2571x2xe2x88x920.5229x+72.69xe2x89xa6yxe2x89xa60.2571x2xe2x88x920.5229x+75.66, 
for the long axis C: 0.5000x2xe2x88x921.0600x+72.99xe2x89xa6yxe2x89xa60.5000x2xe2x88x921.0600x+75.96, 
wherein x denotes a position on the diagonal, short or long axes.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.